Role of Gelsolin in the Formation and Organization of Triton-Soluble F-Actin During Myeloid Differentiation of HL-60 Cells

Structurally and functionally distinct F-actin pools coexist with globular (G)-actin in a variety of eukaryotic cells, including polymorphonuclear leukocytes (PMNs). In PMNs. a Triton-soluble F-actin pool (TSF) exists as short cytoplasmic filaments capped with gelsolin, while Triton-insoluble F-actin (TIF) is a three-dimensional meshwork of F-actin associated with actin-binding protein 280 (ABP-280), a-actinin, and tropomyosin. The unique association of gelsolin with the TSF suggests a role for gelsolin in creation or regulation of TSF. To evaluate gelsolin's role in TSF formation, the quantities of actin and gelsolin were determined by quantitative sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblots in uninduced HL-60 cells (UHL-60) and in HL-60 cells induced to myeloid differentiation with 1,25% dimethyl sulfoxide for 4 to 5 days (I-HL-60). UHL-60 cells contain 17.76 f 6.01 pmol actin per 10' cells (TIF, 5.3 5 1.5; TSF, 2.17 f 0.37; G, 10.3 2 5.7; n = 5) and 0.073 pmol gelsolin per IO' cells (TIF, 0; TSF, 0.002 5 0.005; G, 0.07 5 0.01; n = 3). representing molar actin to gelsolin (A:G) ratios of 1,085:l for TSF and 147:l for G. After myeloid differ-